Independent runtime math
Backup power, measured in usable kilowatt-hours.
Every battery is sold on the number printed on the box. What reaches your outlet is smaller, and what your sump pump or refrigerator actually needs is a different number again. We publish all three, with the arithmetic shown, for every appliance and every unit we rank.
Start with your problem
Featured
Battery backup for a garage door opener: one cycle is about 4 Wh, so buy for the start, not the hours
LiftMaster rates a 1/2 HP opener at 6 A and a cycle takes 22 seconds: ten a day is 44 Wh. What the built-in battery does, and five units that clear the start.
Read the article →How we measure
Sourced specs, shown math, no guesses.
Brands answer "will it run my fridge" about their own product. We answer it with the maker's spec sheet, a stated efficiency, and an appliance's real running and surge draw, then print the assumptions.
- 01
Usable, not advertised
Every unit is described by what reaches the outlet after inverter loss and the depth-of-discharge limit, with the sticker number beside it for comparison.
- 02
Surge before capacity
A pump draws three to five times its running watts at start. We check the inverter's surge rating first, because that is what trips, not the watt-hours.
- 03
Certification stated plainly
UL 2743, UL 9540 and UL 1973 are named when a product carries them and "none stated" when it does not. An uncertified import is never presented as equivalent.
- 04
Dated, sourced, human-checked
Each card carries the model number and the day we read its spec sheet. Photos come from the retailer, never generated, and a person reviews every page.
Latest
-
3-day power outage plan by house size: what to keep on, and how many kilowatt-hours that is
Four households, apartment to well-and-sump farmhouse, each with an essentials list in watt-hours a day and the battery class that covers three days.
-
Anker SOLIX F3800 vs EcoFlow DELTA Pro Ultra: the two 240 V portables, one spec sheet each
The two portables that output 240 V from one unit, line by line from their makers' pages: capacity, output, what each states about surge and listings.
-
Battery backup for a Wi-Fi router: the smallest unit that keeps the internet on, with the hours worked out
A router draws about 30 W by its adapter rating, so a 288 Wh unit is a working day and a 1 kWh unit a weekend. Five UPS-capable picks, sized from the label.
-
Battery backup for a window AC: hours per kWh at 8,000 BTU, and the surge rule that decides the unit
An 8,000 BTU window AC draws 533 W running by its ENERGY STAR figure and cycles about half the time. Five units that clear the compressor rule, with hours.
-
Best expandable power station: five systems that grow past 3 kWh, ranked on what they can start
The expandable class ranked on 240 V output, stated surge, expansion ceiling and safety listing: which systems start a well pump and which stay 120 V.
-
Best 1 kWh power station: five units for a day of essentials, ranked on the spec sheet
The 1 kWh class ranked on usable watt-hours, inverter headroom, UPS switchover and the cycle basis each maker actually states, every figure dated.
-
Best 2 kWh power station: five units ranked by what reaches the outlet
The 2 kWh class ranked on usable watt-hours, surge headroom, cycle rating and stated certification, every spec read from the maker's page and dated.
-
Best solar generator: five station-and-panel kits ranked by what a day of sun puts back
Five power station and panel kits ranked on usable watt-hours, the panel's real output at the maker's own 75% figure, refill hours and the unit's solar ceiling.
-
Can you fly with a power station? The FAA's watt-hour lines, and what they mean for every unit on this site
The FAA's three watt-hour tiers for lithium batteries, why almost no power station clears them, the airline-approval band, and what a CPAP traveler packs.
-
How long do power stations last? Cycles, calendar years and the shelf, from the makers' own figures
What a cycle rating promises and to what capacity, how calendar aging and storage habits shorten it, and EcoFlow's published storage rules.
-
How many watts does a chest freezer use? Three ENERGY STAR sizes, and what they mean in an outage
Average draw for 10, 16 and 22 cubic foot chest freezers from their ENERGY STAR listings, the compressor start-up caveat, and USDA's 48-hour rule.
-
How many watts does a well pump use? Franklin's motor table, running and locked rotor
Running watts and locked-rotor start for 1/3 to 1 HP well pump motors from Franklin Electric's data, the duty cycle from real water use, and the battery math.
-
Pass-through charging and UPS mode explained: leaving the battery plugged in so the outage finds it full
What pass-through charging is, how a power station's UPS mode differs from a real UPS, the switchover times makers state, and how to set one up.
-
Power outage food safety: the USDA clock for the refrigerator and freezer, and what a battery buys you
USDA's windows for a closed refrigerator and freezer, the 40 F and two-hour discard rule, what refreezes and what does not, and how a battery moves the clock.
-
Solar panel watts vs real charge time: why a 400 W panel is a 300 W panel, and what that does to your day
What a panel's rated watts mean, EcoFlow's own figure for real output, each power station's solar input ceiling, and the sun-hours a refill actually takes.
-
UL 2743, UL 9540 and UL 1973 explained: what a power station's safety listing actually covers
The three listings that matter for home batteries in UL's own scope language, why a UL94 flame rating is not one of them, and which makers state what.
-
Watt-hours explained for homeowners: the one unit every backup decision runs on
Watts, watt-hours and kilowatt-hours in plain terms, the conversions from amps and volts, and the two mistakes that oversize or undersize a backup battery.
-
Battery backup for a refrigerator: how long a power station keeps food cold, from the EnergyGuide number
Hours a 1, 2 or 4 kWh power station keeps a refrigerator cold, sized from the EnergyGuide label, and five units with UPS switchover to do it unattended.
-
Battery backup for a space heater: do not do this, and here is what to do instead
A 1,500 W heater empties a 2 kWh power station in about an hour. The arithmetic from the heater's nameplate, and the loads that keep a person warm instead.
-
Generator for a well pump: battery or gas, sized from the motor's locked-rotor amps
Franklin publishes 5 A running and 32.2 A locked rotor for a 1/2 HP well pump motor. What that means for a generator, and the two batteries that clear it.
-
Home battery backup: the three classes, what each actually runs, and how to size yours
Portable, expandable and installed home batteries compared on what they run and for how long, sized in kilowatt-hours per outage day from sourced figures.
-
Home battery vs standby generator: the same outage, two very different machines
Runtime, fuel, noise, start-up power and safety from the makers' own figures: a 22 kW Generac against Powerwall 3 and aPower 2, and when both is the answer.
-
How a transfer switch works, and why every backup source that feeds a circuit needs one
Manual and automatic transfer switches, interlocks, inlets and smart panels explained, why backfeeding is dangerous, and what an electrician installs.
-
How many watts does a refrigerator use? Read it off the yellow label
The EnergyGuide method for a real average draw, two ENERGY STAR models worked through, and why the compressor's start-up spike is not on the label.
-
LiFePO4 vs NMC power stations: what the chemistry changes, in the makers' own numbers
Cycle life, weight, cold behaviour and what a cycle rating actually promises, compared on two Jackery units that differ mainly in chemistry.
-
Portable power station for a CPAP: how many nights, from ResMed's own power figures
Runtime for a CPAP with and without the humidifier, computed from ResMed's published draw, and five buyable units ranked for a night, a weekend and a week.
-
Whole house battery backup: sizing an installed system, with or without solar
How installed home batteries are sized from your utility bill and your biggest motor, what Powerwall 3 and aPower 2 promise, and the without-solar case.
-
Winter storm power outage plan: what to power, in what order, for how many days
A priority list in watt-hours: refrigerator, CPAP, phones and sump pump before anything that makes heat, with USDA food windows and three-day battery math.
-
Battery backup for a sump pump: what actually works, sized from the pump's own numbers
Sized from a real pump's nameplate, not the box: which power stations run a 1/3 HP sump pump through a night of rain, and for how long.
-
How many watts does a sump pump use? Four real pumps, from the nameplate
Running watts for four common sump pumps from the makers' spec sheets, the one published locked-rotor figure, and the math from watts to a night's watt-hours.
-
Running watts vs surge watts: the number that trips a battery before capacity ever matters
What continuous and surge ratings promise, why motors spike at start-up, how to read locked-rotor amps, and why boost modes do not count for a pump.
-
Usable capacity vs advertised: why a 2,048 Wh battery delivers about 1,740 Wh at the outlet
Where the watt-hours go between the sticker and your appliance: depth of discharge, inverter loss and idle draw, and the formula the makers themselves publish.